The purpose of this research is to link variability in the phenotypic expression of specific markers of abnormal brain function in individuals with Williams syndrome to variability in brain structure, medical profile, and genetic profile as determined ina the other projects of this program project. We have identified two markers of brain function linked to abnormal auditory language and sensory processing typical of individuals with Williams syndrome. Additionally, we have developed a new paradigm to study brain function linked to one aspect of spatial cognition that has been the subject of extensive behavioral research on Williams syndrome, i.e., face recognition. We will explore the variability in the phenotypic expression of these markers of brain function and compare cerebral organization during language and non-language cognitive tasks in individuals with Williams syndrome. The results will be compared to those of normally developing children. Additional comparisons of children with Down syndrome will aid ina the separation of different aspects of neural development linked to retardation, delayed acquisition of language, and chronological age. We will record event-related brain potentials (ERPs) from over several regions between and within the hemispheres as children with Williams syndrome, Down syndrome, and normal children aged 10-22 years as they process sensory, cognitive, and language information in tasks designed to modulate different and specific types of processing. Behavioral and ERP data from these experiments will be compared with behavioral measures from standardized tests of language and cognitive capabilities and to measures of brain structure. In the case of children with Williams syndrome, we will explore how the variability in the expression of the phenotypic markers of brain function may be linked with the incidence of specific genetic abnormalities observed in these individuals.